As for the firmware I recommend akaio and all you do is drag the __aio folder and akmenu4.nds on to the root of the card you can also put the official loader in the ak2loader subfolder within the __aio folder for better game compatibility.

Unzip the firmware. You'll see a file named "akmenu4.nds" and a folder named either "__ak2" or "__aio" depending on which firmware you're using.

Place the file and folder (along with its contents) onto your microSD card. Make a folder named "games" and place a few .nds files in it.

Always use the "safely remove hardware" option to remove the microSD card from your computer.

Insert the AK2 into your DS. Insert the microSD card into the AK2.

Turn it on. Navigate to your "games" folder and select a game to run. Click the game's icon with the stylus to run it. You can also change game options by using the "start" menu with the game selected.

The official firmware uses the Bliss menu (which Bliss is no longer developing).

AKAIO is a different menu which has all of the features of Bliss and then some. AKAIO is being actively developed by Smiths and Normmatt, and runs on both the AK2 and the AKRPG (which is why it's named AIO -- All in One).

Gelu also has his own menu for the RPG only. Gelu's changes to his menu are usually incorporated into AKAIO.